The present invention is related to electronic audio distribution systems that accept a plurality of audio inputs from sources such as microphones and produce a plurality of audio outputs representative of a mixed audio signal.
Public address and sound systems often employ multiple input audio systems to accept and process multiple audio inputs to produce a combined output signal. Prior art multiple input systems accept audio inputs from microphones, musical instruments, amplifier outputs and the like and produce a combined output that is then distributed to a plurality of speakers for broadcast. These systems are particularly advantageous for use in large areas such as meeting halls, concert venues, boardrooms, airport terminals, and train and bus stations.
Some prior art signal processing systems employ various signal attenuation arrangements whereby the signal output from the system is attenuated based on the number of active signal inputs to avoid undesirable distortion and/or feedback effects. Many prior art attenuation systems produce a reference signal derived from sensing the ambient noise level in an area proximate the sound system. This reference signal is then compared to an audio input source to determine whether that audio source should be activated as an input to the system. Furthermore, some prior art systems employ circuitry arrangements whereby the total gain of the system remains constant at all times.
Furthermore, many prior art systems employ various gating mechanisms to turn on audio input sources when an audio signal is present that is desirable to amplify, while gating the source input off when only ambient or background noise is present. Many of these prior art gating mechanisms often clip or cut off the beginning of the audible input, because the systems do not discriminate between desirable and undesirable inputs quickly enough.
Additionally, many signal processing systems accept a plurality of analog signal sources for processing using digital circuitry. The incoming analog signals are digitized and processed according to a plurality of programmable or configurable system parameters, whereupon the resultant digital outputs are converted back into analog signals to drive various sound transducers such as loudspeakers. The vast majority of these prior art systems suffer from crosstalk and system noise as a result of the commingling of analog and digital signal data. Furthermore, many prior art devices are limited in their ability to accept low-level audio input signals such as microphone inputs due to the noise floor of the system. Techniques for reduction of system noise are typically limited to enhanced shielding of signals to reduce noise throughout.
The instant invention obviates the aforementioned problems by providing a digital signal processing system having multiple analog audio signal inputs and outputs for providing distributed audio to a user-defined broadcast environment. The system is configurable and adaptable for use in a wide variety of audio mixing applications, from conference rooms, to boardrooms, to large venues. A mainframe chassis that may be mounted in a standard electronics equipment rack is provided having a plurality of slots therein to house a plurality of printed circuit board cards. The chassis includes a backplane that transmits digital signals between the component cards installed in the chassis slots.
The system includes a central processor card having a microprocessor with associated memory that accepts system software instructions and communicates with the other component cards in the system. The central processor card further includes a plurality of on-board digital signal processors and associated multi-port memory for handling all system audio data processing. The multi-port memory allows sharing of data between a plurality of the digital signal processors in the system, thereby providing for efficient parallel processing.
A plurality of analog input cards are used to accept analog audio signals from various sources throughout the application environment. While most audio inputs are conventional microphone signals, the input cards may be configured to accept signals from a variety of audio sources. The analog input cards further include analog to digital converters electronics thereon to convert the analog input signals to a digital data representation.
Additionally, a plurality of analog output cards are employed to produce mixed audio outputs to drive, for example, a plurality of speakers in a venue. The analog output cards include digital to analog converters to convert processed (mixed) digital output to an analog output suitable for sound reproduction. Furthermore, the analog output cards are configurable to permit line level, line driver or amplifier analog output signals.
In addition to the central processing card, both the analog output and input cards include on-board microprocessors and digital signal processors that communicate on a plurality of system busses through the chassis backplane. The digital signal processors on the central processing card are capable of transmitting and receiving data to and from the multi-port memory thereon. This sharing of data memory is made particularly efficient by a data memory page-swapping technique that enables efficient throughput of all audio data, even when operated on by digital signal processors on a plurality of system cards.
The invention provides the ability for a user to configure the system to accept and produce a plurality of inputs and outputs respectively, and permits a user to program various audio processing objects such as mixers, compressors, limiters, and equalizers to name a few. The audio objects are processed by the signal processors resident in the system to produce a resultant audio output or outputs with minimal propagation delays.
Additionally, the unique configuration of the analog input and output cards and the orientation of the chassis backplane permit complete isolation of analog and digital signals in the system, thereby greatly reducing noise and cross-talk.
Therefore, it is an object of the present invention to provide an electronic system for processing audio input signals and producing mixed audio output signals.
It is a further object of the invention to provide a digital audio processor having a plurality of analog inputs and outputs.
It is a further object of the invention to provide a digital audio processor having complete separation of digital and analog signals therein.
It is a further object of the invention to provide a digital audio processor having minimal signal propagation delays from input to output.
Other objects and advantages of the instant invention will be apparent after reading the detailed description of the preferred embodiments, taken in conjunction with the accompanying drawing figures.